Incidence of COVID-19-Associated Hospitalization by Vaccination Status in Children and Adolescents During Omicron-Dominant Period in Japan: The VENUS Study.

Background/

Objectives

Evidence regarding the impact of COVID-19 vaccination on children and adolescents remains limited, particularly in Japan. Thus, this study aimed to estimate incidence rates of COVID-19-associated hospitalization by vaccination status and evaluate the association between COVID-19 vaccination and COVID-19-associated hospitalization among individuals aged 6 months to <18 years in Japan.

Methods

We conducted a retrospective, population-based cohort study using linked health insurance claims data and municipal COVID-19 vaccination registry records from nine Japanese municipalities between 1 January 2022, and 31 March 2023, when the Omicron variant was dominant nationwide. Incidence rates of COVID-19-associated hospitalization were estimated among unvaccinated individuals and those who had received one dose (partially vaccinated) or at least two doses of an ancestral monovalent COVID-19 vaccine (fully vaccinated). Incidence rate ratios (IRRs) were calculated, adjusting for age group, sex, presence of underlying medical conditions, municipality, and calendar month.

Results

Among 163,305 individuals, 93 COVID-19-associated hospitalizations were identified. Crude incidence rates were 4.5 (95% confidence interval [CI]: 3.6-5.6), 3.2 (95% CI: 0.1-18.0), and 2.3 (95% CI: 1.1-4.2) per 100,000 person-months in unvaccinated, partially, and fully vaccinated groups, respectively. The adjusted IRR for the fully vaccinated group was 0.429 (95% CI: 0.198-0.930). Among hospitalized patients, 30.1% had underlying medical conditions, and only 4.3% required oxygen administration during hospitalization.

Conclusions

Receiving at least two doses of COVID-19 vaccine was associated with a lower incidence rate of COVID-19-associated hospitalization among children and adolescents during the Omicron-dominant period in Japan. Expanding vaccine uptake among eligible pediatric populations may help reduce the burden of severe disease.